Light emitting modules, for example light emitting diode (LED) arrays, are widely used in optoelectronic devices of image processing apparatus such as printing machines, copying machines or scanning machines.
Referring to FIGS. 1 and 2, a packaged structure of a conventional LED module is partially shown. The LED module comprises a substrate 111, a plurality of light emitting elements 121 adhered to the substrate 111 with adhesive material 151 and separate from one another for independently emitting light, and a plurality of driving circuit chips 131 adhered to the substrate 111 with adhesive material 152 and separate from one another for independently driving said light emitting elements 121. The driving circuit chips 131 are electrically connected to the light emitting elements 121 via bonding wires 141, respectively. The driving circuit chips 131 are further electrically connected to other elements on the substrate 111 via bonding wires 161.
Since the light emitting elements 121 and the driving circuit chips 131 are bonded to each other one on one with individual gold wires, there would be numerous wire bonding operations required to be performed in the manufacturing process of a light emitting module. Take an A4 size LED printer head for example. In order to accomplish a resolution of 600 dpi, about 5,000 pairs of I/O sites of the light emitting elements 121 and the driving circuit chips 131 need be connected together. In other words, about 5,000 wire bonding operations need be performed in order to complete the connection of the light emitting elements 121 with the driving circuit chips 131. The large number of wire bonding operations complicates the manufacturing process of the light emitting diode and thus adverse to the yield and manufacturing cost. If higher resolution is required, the number of wire-bonding operations need be increased accordingly. Currently, the reliable bonding pitch in a pad is about 100 micrometers. If the wiring density is further increased, the pitch will become less and thus the manufacturing of the device would become more difficult and costly.